1. Technical Field
The present invention relates to pump sprayers, and more particularly, to sprayers of the type which employ an expandable accumulator as a pressure source for discharging fluid from a spray nozzle.
2. Background Art
Compressed air sprayers which employ a manually operated piston air pump are commonly used for dispensing fluids such as insecticides, herbicides, sealants, cleaning fluids and other liquids. Such sprayers normally include a specially designed container, tank or bottle which serves both to hold the fluid to be dispensed and to act as a pressure vessel (i.e., the pressure source for the liquid). Such conventional containers, of course, have a fixed volume.
In operation of a compressed air sprayer, the air pump pumps air from outside the container to inside the container. Initially, the fluid and air in the container is at ambient pressure. As air is pumped into the container, the air in the container is compressed. The compressed air acts as a spring on the fluid and provides a pressure source for discharging fluid from the container.
One problem in pump sprayers having conventional compressed air containers is that the pressure exerted on the fluid in the container does not remain constant as the fluid is dispensed and the volume of fluid in the container changes. There is a continuously decreasing discharge pressure as fluid in the container is discharged, and this characteristic results in the requirement for a relatively high container pressure to achieve an extended spray duration. Further, if a constant spray rate is required, a pressure regulator must be used with the sprayer, and the addition of a pressure regulator adds to the expense of the sprayer. Also, compressing air is an inefficient way of storing energy to provide the motive force for the sprayer.
Another problem in known compressed air sprayers is that the supply container must be thoroughly cleaned after it is used with one chemical before a different chemical can be dispensed. In some cases, an unused chemical must be removed from the supply container and stored for future applications. Such cleaning and storage of chemicals is messy, time consuming and costly. A sprayer apparatus has been designed to operate with standard containers which can be used once and discarded after a particular application. These standard refill containers are normally of relatively light construction, and thus are only suitable for low pressure applications, such as trigger sprayer applications. However unlike trigger sprayers, compressed air sprayers operate under significantly greater pressures which requires heavy gauge, reinforced steel or plastic containers. Thus, standard, lightweight, refill containers have not been proposed or even suggested for compressed air sprayer applications.
A trigger sprayer, employing standard refill containers is shown in the patent to Pauls et al., U.S. Pat. No. 4,241,853. The trigger pump mechanism is attached to the top of the standard container. The pump mechanism includes a resilient bladder which is charged with fluid drawn from the container by means of a piston pump. Fluid can be dispensed from the bladder in a continuous stream or in an intermittent discharge. A disadvantage of the Pauls et al. device is that all of the pump structure is located outside the container, with the exception of a dip tube which extends into the liquid. As a result of such construction, the volume of the liquid dispensed is limited by the relatively small pump and bladder. In addition, the palm/finger actuation of the trigger mechanism to charge the Pauls device is fatiguing and may, with repetitive use, contribute to medical problems such as carpal tunnel syndrome. Further, the grouping of all of the working components above and outside the container substantially increases the complexity of the dispenser.